Dry sowing inoculant rates double

The other alternative is to use a granular inoculant which delivers a high number of rhizobia at sowing to increase the likelihood of successful nodulation and nitrogen fixation.

This approach can allow growers in drier climates more flexibility when sowing pulses in suboptimal conditions.

SA Research and Development Institute (SARDI) senior research officer Liz Farquharson said pulse grain prices and nitrogen fixation benefits made pulses an attractive crop option.

However, dry sowing could hinder the survival of the applied rhizobia bacteria as they were sensitive to desiccation.

The longer the 'dry period' between sowing and germinating rains, the higher the risk of an inoculation failure.

"Dry sowing is less of a concern where a legume nodulated by the same rhizobia group has been grown recently in the paddock and the soil is favourable to rhizobia survival," Dr Farquharson said.

"In these conditions, the risk of nodulation failure is much lower."

Research to optimise legume inoculation for dry sowing is included in the Grains Research and Development Corporation (GRDC) investment, 'Increasing nitrogen fixation in pulse crops through the development of improved rhizobial strains, inoculation and crop management practices'.

Inoculants that carry the 'Green Tick' logo approved by the Australian Inoculants Research Group meet minimum quality standards for purity and number of rhizobia per gram of product.

This rating will soon be available for granules.

Dry sowing is discouraged on hostile soils, especially acid soils (pHca 6.0) for bean, lentil and pea.

Dr Farquharson also advised growers to take particular care if they intend to inoculate seed treated with pesticides.

"Where pesticide application is necessary, the rhizobia are best applied to seed as close to sowing as is possible and sown into moist soil, or granular inoculant may provide a better option as this reduces direct exposure of the rhizobia to the pesticide," she said.

The project will also develop enhanced inoculation and crop management practices to maximise nitrogen fixation in suboptimal conditions and avoid any impact of crop protection chemicals and fertiliser on nodulation.

This includes the development and release of improved rhizobia for bean and lentil on acid soils.

It is hoped the new rhizobia strain will have a substantial impact in the southern cropping region where pulse production is expanding into high rainfall areas with characteristically low pH soils.